The Predictors Study began in 1989 as a longitudinal, observational study of disease course in patients with Alzheimer's disease. The original hypothesis was that noncognitive signs and symptoms that occur in a significant number of patients with Alzheimer's disease have utility in predicting disease course. These hypotheses have been confirmed, and the investigators now plan to prospectively valildate and expand this predictor model by recruiting a new cohort of subjects. The patient population will also be expanded to include patients suffering from dementia with Lewy bodies. Dementia due to Alzheimer's disease and Lewy body disease are degenerative brain disorders that result in progressive decline of intellect and functional capacity. Although these diseases are incurable, improved patient management may be achieved through accurate prediction of disease course. This information may be of use to families to aid in the planning of personal and financial matters. The study involves the collaboration of three sites: Columbia University, Johns Hopkins University, and Harvard Medical School. All sites follow identical procedures. Subjects are evaluated at six month intervals. At each visit, patients receive assessments of intellectual capacity, functional skills, and level of dependence. The presence and severity of predictive clinical signs (i.e., extrapyramidal signs, myoclonus, and psychosis) also are rated.